As the cross dispersion, the two-dimensional spectrum of echelle spectrometer cannot calibrate the wavelength spectrum directly, therefore the spectrum reduction model for the transmission prism echelle spectrometer with the C-T structure is built. The dispersion rule and relationship between prism and echelle is analyzed, and the relational expression of wavelength and image coordinates is also established. According to the optical structure and optical transmission characteristics, the deviation of coordinates caused by the element can be regulated, and the accurate image coordinates can be calculated. Finally the spectrum reduction model is accomplished. This model can recover the two-dimensional spectrum of echelle spectrometer quickly and accurately, and calibrate the wavelength. The error of image coordinates calculated by the model is less than one pixel.Key words